Schistosomiasis: an epidemiological update on Brazil's southernmost low endemic area in Esteio

Abstract INTRODUCTION: Brazil’s southernmost state, Rio Grande do Sul (RGS), was considered schistosomiasis-free until 1998 when a low endemic focus was identified in Esteio, a city located next to the capital of RGS. In the last two decades, the control interventions applied in the region have been apparently successful, and the absence of new cases indicated the possibility of interrupted schistosomiasis transmission. The objective of this study was to update the clinical and epidemiological data of schistosomiasis in Esteio. METHODS: We reviewed all 28 individuals diagnosed with the infection since 1997 and a survey was applied to a group of 29 school-aged children residing in Vila Pedreira, one of the most affected neighborhoods. RESULTS No eggs were detected in fecal samples using the Helmintex method, and all samples were negative for serum antibodies on examination by the western blot technique using the Schistosoma mansoni microsomal antigen (MAMA- WB). In contrast, 23 individuals (79%) tested positive for the cathodic circulating antigen with the point-of-care immunochromatographic test (POC-CCA) on urine samples. Of the 28 formerly infected individuals, only eight were located, of which four tested positive, and four tested negative for serum antibodies using the MAMA-WB technique. CONCLUSIONS: Current adverse conditions for S. mansoni transmission in Esteio and the absence of a confirmed diagnosis suggests that there is (i) a lack of specificity of the POC-CCA test in low endemic settings, and (ii) a high probability that interruption of schistosomiasis has been achieved in Esteio.

**摘要与引言**：巴西南部最南端的南里奥格兰德州（Rio Grande do Sul, RGS）曾被认为无血吸虫病流行，直至1998年在毗邻该州首府的埃斯特奥市（Esteio）发现一处低流行疫点。近二十年来，当地实施的血吸虫病防控干预措施成效显著，未再报告新增病例，提示该病传播或已中断。本研究旨在更新埃斯特奥市血吸虫病的临床与流行病学数据。
**方法**：本研究回顾了1997年以来确诊感染的全部28名患者，并对居住在受影响最严重街区之一的佩德拉村（Vila Pedreira）的29名学龄儿童开展了流行病学调查。
**结果**：采用赫尔明特克斯法（Helmintex）检测粪便样本，未检出血吸虫卵；采用曼氏血吸虫微粒体抗原-蛋白质印迹法（MAMA-WB）检测血清抗体，所有样本均呈阴性。与之相对，采用即时免疫层析试验（POC-CCA）检测尿液样本中的循环阴极抗原时，23名受试者（占比79%）结果呈阳性。在28名既往感染者中，仅追踪到8名，其中4名经MAMA-WB技术检测血清抗体呈阳性，其余4名呈阴性。
**结论**：埃斯特奥市当前不利于曼氏血吸虫（S. mansoni）传播的环境条件，以及未出现确诊病例的现状，提示两点结论：其一，即时免疫层析试验（POC-CCA）在低流行环境中缺乏特异性；其二，埃斯特奥市血吸虫病传播已被阻断的可能性极高。